Android Auto now lets you customize your app drawer0
pkoya1 (via XDA Developers) claims Google now lets Android Auto users choose which apps they want to appear in the app drawer. Unfortunately, the new feature is not available for everyone yet, and trying to download the Android Auto app from the Google Play Store won't help.
It looks like this is a server-side update that will be pushed out in waves, so it will probably take some time to reach all customers. In the screenshot attached to the article, several apps can be selected to appear in the Android Auto app drawer.
Some of them like Google Play Music or Maps can't be removed since they are core system apps. However, depending on what phone you use, you might be able to uninstall Google Play Music if you'd rather use Spotify instead. Keep an eye out on the new feature if you're using Android Auto and start customizing the app drawer as soon as you have the option.